Getter-ion pump for producing and maintaining a high vacuum



Jan. 13, 1970 MAXJOSEF SCHDNHUBER (BETTER-ION PUMP FOR PRODUCING ANDMAINTAINING A HIGH VACUUM 5 Sheets-Sheet 1 Filed Aug. 5, 1968 Fig.7

Fig.5

3, 1970 MAX-JOSEF SCHONHUBER 3,489,336

GETTER-ION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM Filed Aug.1968 5 Sheets-Sheet 2 UL z0 3 14 14 A i E? 4 I Fig. 2

Jan. 13, 1970 MAXJOSEF SCHONHU-BER 3,489,336

GETTER-ION PUMP FOR ERODUCING AND MAINTAINING A HIGH VACUUM Filed Aug.5, 1968 5 Sheets-Sheet 3 Jan. 13, 1970 MAX-JOSEF SCHONHU BER ,489,336

GETTERION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM I Filed Aug.5, 1968 5 Sheets-Sheet 4 1970 MAX-JOSEF SCHONHUBER 3,489,336

GETTERION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM Filed Aug. 5,1968 5 Sheets-Sheet 5 28 u u [1 H96 United States Patent 3,489,336GETTER-ION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM Max-JosefSchiinhuber, 1 Seefeldquai, 8008 Zurich, Switzerland Filed Aug. 5, 1968,Ser. No. 750,442 Claims priority, application Switzerland, Aug. 25,1967, 11,995/ 67 Int. Cl. FtMh 37/02; H01j 7/16 US. Cl. 230-69 16 ClaimsABSTRACT OF THE DISCLOSURE The invention concerns a getter-ion pump forproducing and maintaining a high vacuum with electrodes between which anelectrical discharge occurs.

Up to now such ion pumps are known as evapor-ion pumps and particularlyas sputter-ion pumps. With evaporion pumps getter material is vaporizedby heating the getter metal wire ohmically and the vaporized materialcondenses on cooler surfaces. These surface films which are for thesorption of non rare gases temporarily very active can to a certainextent be used for pumping away also rare gases, but only when theiratoms are ionized by the application of an electrical voltage and aretransported as positive ions to the negatively charged surfacecondensate which constantly renews itself and where the ions then areburied. The sputter-ion pumps also operate with a discharge, a so-calledlow current high voltage Penning discharge. The electrons ionize the gasparticles and then by means of an electrical field acting in thedirection of the cathode the positive ions are accelerated to severalthousand volts and shot into the cathode which consists of gettermaterial, for instance titanium, or continuously sputter the cathodesurface. Already in view of this cleanup mechanism it is understandablethat also here the rare gas atoms, which do not combine chemically withthe getter material, can only be pumped away at a much lower speed. Inthe long run, these noble gas atoms are finally pumped away, mainly inthe inaccessible precipitation due to sputtering which is not subjectedtofurther sputtering.

The electron paths are extended in order to increase the pumping effectover a larger pressure range. This is achieved by means of magneticfields which give the electrons a circular movement and thus lengthenthe path between the electrodes (anode and cathode). The anode is givena cellular construction, so that the electrons can travel several timesalong the anode surfaces. In addition to the magnetic field for thepurpose of obtaining a considerable increase in pump speed it is,however, necessary here to connect a large number of cells and electrodepairs in parallel and also complicated cathode constructions have to betaken into account.

These pumps, quite apart from a heavy magnet and a continuously appliedhigh voltage of many thousand volts, can thus only achieve an adequatepumping speed also for rare gases when used in conjunction with severalpairs of electrodes operating in parallel or when several pump units areconnected together in parallel. The surface of the cathode material cannamely only be bombarded by 3,489,336 Patented Jan. 13, 1970 "ice therare gases for a certain time and up to a definite degree of saturation.Due to sputtering of the cathode material during the pumping process,gas molecules which have been shot into the cathode are released againso that after a comparatively short operation time a state ofequilibrium is more or less reached between the ingoing and outgoingions. In the end therefore the rare gas atoms continuously buried in theinaccessible precipitation due to sputtering, determine to a greatextent the pump speed for rare gases.

The application of a powerful magnetic field with a heavy magnet forlengthening the electron path as well as the necessary parallelconnection of cells and electrodes of getter material necessitate a veryconsiderable outlay. Newer methods working with different cathode gettermaterials having different sputtering rates can only to a slighterextent increase the pumping speed for rare gases.

It has now been observed that with a high current arc discharge it ispossible to obtain a pumping effect with all gases which is severalorders of magnitude better per surface unit whereby a high vacuum canthus also be obtained for rare gases within a minimum of time. Inaccordance with the invention it is therefore proposed that means areprovided which when switching on the pump, produce a cathode spot andarc between the electrodes also in the high vacuum region, further meansbeing also provided which enlarge the arc as regards the current andmaintain and prolong it after ignition and divide the original cathodespot into several spots. The cathode spot which forms melts the metal ofthe electrodes, which can consist of titanium, zirconium, tantal orother getter materials, at local microscopically small points andvaporizes it, so that the locally necessary gas atmosphere is presenteven in the high and ultra-high vacuum range. The are discharge can thencontinue with only a small electrode voltage and ionize the gasparticles which come from the volume that has to be evacuated andtransport them to the cathode surface with an energy corresponding tothe cathode fall. There, due to the continuous motion of the cathodespot, the metal parts which have temporarily become liquified in thespot immediately become solidified again thereby enclosing the gasmolecules in the much deeper cathode surface layers than is possiblewith a highvoltage Penning discharge, for example sputter-ion pumps. Oncondition that the cathode spot (arc discharge) has an adequate surfacefor its motion and to enable it to subdivide into several spots (partialarcs), this being possible when the electrodes have a suitable form, apumping speed is attained which is higher than that of other getter-ionpumps of the same size. Moreover, this result is achieved withoutadditional magnetic fields and, as tests have shown, already with only asingle pair of electrodes even when these do not consist of acomplicated construction and an expensive getter material. Due to theultra rapid pumping effect, even in the case of rare gases and to thesame extent as with other gases, it has been verified by tests that ashort pumping operation of only a few seconds is sufficient to reducepermanently the partial pressure of a rare gas of a vacuum plant to forinstance 10- Torr, and also during disconnections of the pump the unraregases in the active surface films caused by the cathode spot as a resultof electrode vaporization are continuously adsorbed and absorbed so thatthe high vacuum is maintained even during longer disconnectionintervals.

Also the total pumpable amount of gas, down to a point where there is anappreciable drop in pump speed, is incomparably greater than that withother getter-ion pumps of the same size because of the gases which arepumped away from a cathode spot are enclosed even in the lower surfacelayers. Therefore the proposed arc getter-ion pump when compared withsputter-ion pumps can also operate with pressures exceeding 10 to 10Torr, that is in the fine or rough vacuum range, and is very suitablefor the rapid evacuation of vacuum vessels of all sizes where a vacuumfree of oil vapour and the like is required Without the use of anycooling traps. Also no water cooling of the pump is necessary in thecase of short time pumping.

Constructional examples of the invention are shown in the accompanyingdrawings. FIG. 1 shows an embodiment with moveable ignition pin. FIGS. 2to 4 are embodiments of the invention without an ignition pin. FIGS. 5and 6 shows two corresponding electrical circuits.

In FIG. 1 the vacuum vessel is indicated by reference number 1. Thegetter-ion pump is mounted on this vessel. It is located in aninsulating cylinder 2 which is provided With a metallic cover 3. Thecathode 4 and the anode 5 between which the arc discharge occurs arelocated in the vessel where there is also an ignition pin 6 which isconnected electrically with the anode 5. This pin consists of a magneticmaterial, whilst the electrodes are of a getter material. Furthermore, acoil 7 is also provided. The device is put into operation by applying avoltage to the anode by way of a bushing insulater 8. At the same timethe coil 7 is connected to a voltage source not shown in the figure,whereby pin 6 is pulled upwards and short circuits the anode andcathode. Then coil 7 is disconnected and the pin is returned to itsinitial position either by means of a spring or due to its own weight.This causes an arc discharge to occur and due to the melting andevaporation of the getter material the necessary' carrier or neutral gasfor a low voltage arc is formed. The surface of the electrodes is solarge that there is sufiicient room to allow the cathode spot to wander.Anode 5 is connected electrically to vessel 1 and is thus at earthpotential. The metallic and insulating parts of the vessel are connectedtogether in a vacuum-tight manner by fused joints. The gas molecules aredrawn from the vacuum vessel 1 into the are by way of openings 9 inanode 5. Screens provided on the insulation cylinder 2 to protect itagainst sputter are not shown. FIG. 2 shows a modified form of theinvention where the length and width of the arc is increased due to theform of the electrodes. In the figure reference number 1 again indicatesthe wall of the vacuum vessel and 2 is the pump wall consisting ofinsulating material and provided with a metallic cover 3. The anode 5 isgrid-shaped to facilitate the passage of the gas residue from the vesselto the pump. The cathode 4 is located only a short distance away fromanode 4. A high voltage pulse is applied here so that an arc occursbetween the electrodes.

A cathode spot thus forms and the getter material melts and evaporateslocally at a microscopically small point, so that a carrier or neutralgas for a low-voltage arc is produced between the electrodes. A lowvoltage of only a few volts thus prevails between the electrodeswhereby, however, a current of several hundred amperes can flow. As aresult, the arc continues to burn and spreads rapidly over the electrodesurface due to the original cathode spot splitting up into severalsmaller cathode spots. The electrodes are prolonged by cylindricalparts, thus cathode 4 by means of a cylinder 10 which extends up tocover 3 for connection to an electrical lead. The actual enlargedelectrode surface extends up to the metallic flange 11 which enlargesthe cylinder at its upper end. Anode 5 is enlarged by means of cylinder12. The actual arc discharge is thus between the outer surface ofcylinder 10 and the inner surface of cylinder 12. The effective surfaceof the cylinders must be larger than the surface of the associatedelectrodes. It need not, however, be more than ten times, because anadditional effect is not to be expected. The spacing between theelectrodes is smaller than between the cylinders. Between flange 11 andthe upper part of cylinder 12 the spacing is also smaller but not sosmall as between the electrodes, so

that the arc cannot come near to the cylinder wall 2. Flange 11 istherefore also as near as possible to cylinder wall 2, but must not comein contact with it. Cathode 4 and anode 5 can consist of gettermaterial, for instance titanium, zirconium or tantal.

The method of operation is as follows: A high voltage pulse is first ofall applied to cylinder 10. Since the distance between the anode andcathode is very small, a breakdown occurs there. Due to the high voltageof many thousand volts this is suificient to produce a cathode spotwhere the getter material at a microscopically small point melts andevaporates and forms a carrier or neutral gas for maintaining an arc.Directly after the voltage pulse, a lower voltage is applied. Thevoltage source must, however, be adequate to enable a current of severalhundred amperes to flow, so that the arc is well supplied. The cathodespot can thus travel over the surface of the electrodes and reaches thecylinder surface where it is driven upwards and then burns with agreater spacing and over a wider surface, that is, longer and wider. Apowerful pumping effect thus occurs which causes the rest of the gas toflow through the opening in the gridshaped electrode 5 into the arc. Themetal which is liquified locally to a microscopic extent in the cathodespot due to the motion of the arc is rapidly solidified again, so thatthe gas molecules become frozen into the cylinder surface. This is notonly the case with active gases which can form chemical compounds withthe metallic electrode but also with rare gases. Therefore, it is nowpossible to evacuate in a simple manner large quantities of rare gasesin vacuum vessels of any size, this being impossible hither-to withconventional pumps.

The effect can be increased, is desired, by cooling the cylinder. Forthis purpose the coolant can be supplied to the inside of the cylindersand discharged again as indicated by the arrows 13, 14 in FIG. 2. Duringa brief pumping time no cooling is, however, necessary.

With the arrangement shown in FIG. 2, the electrodes extend into thevacuum vessel. The ion-getter pump can also be constructed so that it iscompletely mounted on the vacuum vessel. Even in this case, wall 2 doesnot need to be entirely of insulation material down to the vessel, butcan'also consist partly of metal:

FIG. 3 shows another embodiment of the invention where the surface ofelectrodes 4 and 5 are enlarged. The associated cylinders 10 and 12 mustthen each consist of two parts having different cross-sections. Theentire extent of the breakdown surface is thus increased without theoverall height of an arrangement becoming greater.

FIG. 4 shows a further constructional example of the invention wherecylinders 10 and 12 are bent back at the upper end 15. In this way it iseasier to prevent metallic vapour from passing from the electrodes tothe space between the insulation wall and the electrode cylinder.

The electrode need not be completely level. It can be curved at theedge, so that the spacing at the edge is considerably greater thanbetween the level parts. This is indicated in FIG. 4 at the point 27.

The thickness of the electrodes, particularly of the cylinder, may not'be less than 2 mm., in order to prevent them from melting.

The electrical diagram of connections is shown in FIG. 5. An A.C.network with branches 16, 17 serves as a source of supply. Thearrangement can of course also be fed from a direct-current source or atwo-phase system in which case care must be taken to ensure that thedirect voltage does not have any harmonics which are too high. Theindividual phases feed, by way of rectifiers 18 and 19, the electricalarrangement for the getterion pump. An iron core 20 carries the coils 21and 22. Coil 21 is connected to branch 16 by Way of a switch 23 and aresistor 24. Coil 22 is connected by way of another switch 25 to theelectrodes 4 and 5 of the getterion pump. Branch 17 is also connected tothe electrodes 4 and 5 by way of rectifiers 19 and blocking rectifiers26 which in the blocking direction stop the high voltage. Since anode 5is earthed, negative pulses and negative potentials are applied to thegetter-ion pump, the former being for igniting the arc and the latterfor maintaining it.

The method of operation is as follows. First of all switches 23 and 25are closed and a direct current then flows through winding 21. Switch 23is opened for the ignition and then a high voltage pulse occurs on coils21 and 22 and thus also at the electrodes. This pulse initiates the arcdischarge in the pump and the circuit for branch 17 is thus closed, sothat a high current can flow over the arc. Rectifiers 26 keep the highvoltage pulse away fro-m rectifiers 19 of branch 17. When pumping isfinished, switch 25 is reopened. Switches 23 and 25 can also be operatedautomatically when a pressure supervising device switches in thearrangement when the vacuum deteriorates and switches it out again whenthe desired vacuum is reached.

A further electronic circuit is shown in FIG. 6 which operates asfollows:

First of all switches 29 and 38 are closed. When pushbutton 35 isactuated, condenser 36 is discharged on the primary winding of ignitioncoil 34 and this latter supplies a high voltage pulse to the electrodes4, 5 of the getter-ion pump, thereby igniting the arc and forming acathode spot. As a result, the circuit of rectifier 31 is closed, sothat a high current can occur which produces a powerful arc dischargewith several cathode spots. The inductance 33 prevents the high voltagepulse from entering the rectifier 31. When the pumping operation iscompleted, switch 29 is opened again. Switch 29 and push button 35 canalso be actuated automatically when a pressure supervising device isprovided which switches in the apparatus when the vacuum deterioratesand disconnects it when the desired vacuum is attained. This automaticequipment is not shown in FIG. 6.

I claim:

1. Getter-ion pump for producing and maintaining a high vacuum by meansof electrodes between which an electrical discharge occurs,characterized in that means are provided which when switching in thepump produces a cathode spot and are between the electrodes also in thehigh vacuum region, further means being also provided which enlarge theare as regards the current and maintain and prolong it after ignitionand divide the original spot into several spots.

2. Getter-ion pump as defined in claim 1, characterized in that the oneelectrode is of the grid-type.

3. Getter-ion pump as defined in claim 1, characterized in that anignition pin is provided which upon switching in connects at least partof the electrodes together and that a coil is provided at the upper endof said ignition pin which lifts it from a stationary electrode, so thatan arc with cathode spot results.

4. Getter-ion pump as defined in claim 1, characterized in that themeans for producing the cathode spot and are comprise a switching devicewhich by way of a pulse transformer applies a voltage to the electrodesso that a cathode spot forms between the electrodes, and that a furtherswitching device is provided which by way of the diodes applies a lowvoltage to said electrodes which enlarge the are as regards the currentand maintain and prolong it and divide the original cathode spot intoseveral spots, and that each electrode is connected to a cylinder whichis arranged coaxially so that the external surface of one cylinder andthe internal surface of the other cylinder form extended electrodesurfaces.

5. Getter-ion pump as defined in claim 1, characterized in thatadditional means are provided which prevent mutual interference betweenthe means for producing the are and those for maintaining the arc.

6. Getter-ion pump as defined in claim 5, characterized in that themeans consist of blocking rectifiers (26).

7. Getter-ion pump as defined in claim 5, characterized in that themeans consist of a coil (33).

8. Getter-ion pump as defined in claim 4, characterized in that thecylinders consist of two parts of different diameter, those having thelarger diameter being connected to the electrodes.

9. Getter-ion pump as defined in claim 4, characterized in that the endsof the cylindrical parts remote from the electrodes are curved.

10. Getter-ion pump as defined in claim 4, characterized in that thecircumferential surface of the cylindrical parts is not greater than tentimes the surface of the associated electrode.

1.1. Getter-ion pump as defined in claim 4, characterized in that thespacing of the cylinders at their end remote from the electrodes issmaller than at any other point of the cylindrical parts.

12. Getter-ion pump as defined in claim 9, characterized in that theinner cylinder (10) at the end remote from the electrodes is providedwith a flange (11) which is nearer to the outer cylinder (12) and theinsulation wall (2) than the cylinders are with respect to each other.

13. Getter-ion pump as defined in claim 4, with a cooling system for theelectrodes, characterized in that the cooling means are provided whichcause the cooling medium to flow to the inside of the cylinders.

14. Getter-ion pump as defined in claim 1, characterized in that theelectrodes are in the form of a plate with a curved edge, so that thespacing at the edge is greater than between the plate-shaped part.

.15. Getter-ion pump as defined in claim 1, characterized in that theelectrodes and cylindrical parts have a thickness of at least 2 mm.

16. Getter-ion pump as defined in claim 1, characterized in that theelectrodes are made of getter material.

References Cited UNITED STATES PATENTS 3,070,283 12/1962 Hall 230-693,198,422 7/1965 Kienel 23069 ROBERT M. WALKER, Primary Examiner U.S.Cl. X.R. 3137

